Observational data suggests that diets high in calcium are associated with lower body weight and/or fat. Increasing calcium intake while decreasing energy intake (dieting) may be associated with greater weight and fat loss. Furthermore, dairy foods, which are rich in calcium (dietary calcium), may be more effective than non-food calcium supplements (calcium pills) in helping people lose weight and fat while dieting. Scientists do not understand how calcium regulates body weight or fat or why calcium in dairy foods may be more effective than calcium in pills in promoting weight and fat loss. There are a few long-term, studies that examine the effect of high calcium intake while dieting on body weight and fat in obese individuals. Some studies also show that weight loss leads to a loss of bone mineral density (BMD). Increasing calcium from supplements while dieting seems to protect BMD. It is unclear why weight loss increases loss of BMD and how increasing calcium from supplements protects BMD. It may be that increasing calcium while dieting, maintains levels of Vitamin D and parathyroid hormone (PTH). Calcium supplements are also associated with lowering blood lipids. There are few studies that have examined the effect of dairy calcium on BMD and blood lipids during weight loss. The aim of this study is to compare three low energy diets: 1) a high calcium dairy food diet; 2) a high calcium supplement diet; and 3) a low calcium diet for six-months. To compare health benefits of dairy and non-dairy sources of calcium the researchers will measure body weight, fat weight, waist circumference, fasting blood lipid levels, BMD, circulating Vitamin D and PTH. Subjects will be 75 obese pre-menopausal females, randomly assigned to one of the diets. Subjects will be required to attend regularly scheduled cognitive behavioral modification classes. Subjects will monitor daily food intake and physical activity. Weight will be measured weekly and body fat, waist circumference, blood lipids, BMD, Vitamin D and PTH will be measured at baseline and six-months. If increasing dairy or non-dairy calcium accelerates weight and fat loss during energy restriction, as hypothesized, increasing dietary calcium in existing weight loss programs would significantly impact the treatment of obesity. Furthermore, if increasing calcium improves blood lipids and maintains BMD it would contribute to the development of new treatments of obesity, and its associated increased risk for heart disease, and for protection of BMD during weight loss. [unreadable] [unreadable] [unreadable]